Waste products from manufacturing processes involving wood construction include saw dust and other wood wastes. In the past these products were burned or disposed of in land fills. More recently these waste wood products have been used as fillers in plastic composite such as polyvinyl chloride [PVC] and other plastic resins. Such uses of these waste products have reduced the consumption of wood and contributed to better environmental uses of such wastes. Due to the availability of wood waste products as described herein their use as additives/fillers of organic polymers has been extensively studied, see e.g.,
Dalvag et al., xe2x80x9cThe Efficiency of Cellulosic Fillers in Common Thermoplastics. Part II. Filling with Process Aids and Coupling Agentsxe2x80x9d, International Journal of Polymeric Materials, 11:9-38 (1985).
Klason et al., xe2x80x9cThe Efficiency of Cellulosic Fillers in Common Thermoplastics. Part I. Filling Without Processings Aids or Coupling Agentsxe2x80x9d, International Journal of Polymeric Material, pp. 159-187 (Mach 1984).
Kokta et al., xe2x80x9cComposites of Poly(Vinyl Chloride) and Wood Fibers. Part II: Effect of Chemical Treatmentxe2x80x9d, Polymer Composites, 11(2):84-89 (April 1990).
Kokta et al., xe2x80x9cComposites of Polyvinyl Chloride-Wood Fibers. I. Effect of Isocyanate as a Bonding Agentxe2x80x9d, Polym. Plast. Technol. Eng., 29(1and2):87-118 (1990).
Kokta et al., xe2x80x9cComposites of Polyvinyl Chloride-Wood Fibers. III. Effect of Silane as Coupling Agentxe2x80x9d, Journal of Vinyl Technology, 12(3):146-153 (September 1990).
Kokta et al., xe2x80x9cUse of Wood Fibers in Thermoplastic Compositesxe2x80x9d, Polymer Composites, 4(4):229-232 (October 1983).
Maldas et al., xe2x80x9cComposites of Polyvinyl Chloride--Wood Fibers: IV. Effect of the Nature of Fibersxe2x80x9d, Journal of Vinyl Technology, 11(2):90-98 (June 1989).
Raj et al., xe2x80x9cUse of Wood Fibers as Filler in Common Thermoplastic Studies on Mechanical Propertiesxe2x80x9d, Science and Engineering of Composite Materials, 1(3):85-98 (1989).
Raj et al., xe2x80x9cUse of Wood Fibers in Thermoplastics. VII. The Effect of Coupling Agents in Polyethylene-Wood Fiber Compositesxe2x80x9d, Journal of Applied Polymer Science, 37:1089-1103 (1989).
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Yam et al., xe2x80x9cComposites From Compounding Wood Fibers With Recycled High Density Polyethylenexe2x80x9d, Polymer Engineering and Science, 30(11):693-699 (June 1990).
Not withstanding the literature, such as noted above, the combining of wood fibers or wood flour with plastics has not been straight forward. For example, see U.S. Pat. No. 6,015,612 issued to Deaner et al which teaches that by the use of heat and pressure wood fibers can be wetted intercellular with plastic resins leading to composites having a Young""s modules higher than neat PVC.
Other patents are directed to the manufacture of structural parts for door frames and the like from composites of PVC and wood fibers/flours, see for example U.S. Pat. No. 5,406,768 issued to Giuseppe et al.
The field of this invention is different in that it involves the manufacture of such structural parts from foamed PVC and wood flour composites. In this regard see U.S. Pat. No. 6,066,680 issued to Cope which teaches the encapsulation of the wood flour with the resin in the form of pellets prior to extrusion of such members. This invention avoids the step of forming pellets, as taught in the patent issued to Cope.
Manufacturing structural members with conventional foamed plastic composites, is typically limited by physical properties of such composites. Such composites have large linear expansion coefficients, low dimensional stability and are subject to significant thermal distortion. Also such composites have insufficient rigidity (E value) and are prone to warping making them unsuitable for door and window frames. More often than not such members have non-wood like or plastic like surfaces which are undesirable in many applications where wood has been typically used in the past, e.g., window frames.
Following the method of the present invention not only reduces the above undesirable characteristics of such foamed composites but produces structural members which are better suited for applications like door and window frames and the like.
The manufacturing method of this invention involves (a) the mixing the wood flour with powdered PVC resin along with other powdered components, such as thermal stabilizers, foaming agents, lubricants, fillers and pigments to obtain a mixture of powders, (b) placing the mixture of powders in a thermal stirring mixer and employing low speed mixing to blend the mixture of powders followed by a higher speed mixing to disperse said powders into a homogeneous blend, (c) placing said homogeneous blend in a cold stirring mixture and mixing at low speeds to prevent agglomeration of the homogeneous blend from the thermal stirring mixer and (d) then adding the homogeneous blend to an extrusion machine and extruding foamed structural shapes.